It is known to have food products such as rations for back-packer, adventurers and military forces, which comprise sealed packages of pre-cooked food. Conveniently, the food is hermetically sealed, within a vacuum; the food can be heated, on demand, since the food will not need to be cooked, as such. Such food products and apparatus are collectively referred to as Meals-Ready-to-Eat (“MRE”). In addition to the above uses, the products can be used as emergency rations for shelters and for heating of non-food products. Whilst meals, ready-to-eat are used extensively in the military as a method of providing meals to soldiers while in the field, they are also finding their way into use by others, such as campers, boaters, and disaster response teams.
Typically meals ready to eat food sachets are provided on a personal basis, since heat transfer issues may arise in larger packages. Food is heated to a sufficient temperature—around 70° C. or more—to make it a more pleasurable experience, compared with eating such food cold, which can incidentally, be done. Furthermore, there is a danger of burning when the outer wall of the exothermic material storage portion is not sufficiently thermally insulated. Accordingly such foods are typically prepared by heating with flameless heaters, using exothermic chemical reactions.
In one known type of flameless ration heater, an exothermic reaction is provided by calcium carbonate, sodium carbonate, calcium oxide and aluminium powder mixture can be employed. In another type of flameless ration heater, readily oxidized metals such as magnesium which is activated by adding water and is contained within a pouch. The iron plays a catalytic role in the heater mix; salt can be added to facilitate the reaction. To activate the reaction, in either case, an amount of water is added.
To heat an MRE meal, an emergency services personnel/explorer/soldier simply inserts the heater and the MRE pouch back in to a bag provided with the heater, adds a required amount of water into the bag in and, a short time later, dinner can be served—typically from the same container in which the product was heated!
As can be seen, both types of known heater generate hydrogen as a by-product, which is undesirable in view of the tendency of hydrogen to cause explosions and burn as a visible flame. Recently, there have been made attempts to reduce or ameliorate the production of hydrogen.
WO2009003481 (Moeller) teaches of a catalytic heating system comprising a main catalyst for flameless catalytic burning of fuel gas and a triggering system for initiating the catalytic burning, the triggering system comprising an electrical power source, but this is not suitable for MRE applications, with temperatures in excess of 300° C. being achieved. Moreover, it would appear problems associated with hydrogen are replaced by problems associated with fuel gas.
Generally, the compositions for heaters as presently known comprise mixtures of powdered substances that are activated by the addition of water whereby to produce heat. These known devices all involve the principle of hydrolytic oxidation of a reactive metal to provide heat; the reactive metal is commonly aluminium with alkaline media, or magnesium, used with a copper alloy and electrolytic solutions. In each of these types of heating units, there is an incidental production of a molar equivalent of hydrogen from the metal. In view of the risk of the hydrogen burning explosively, this by-product is unwanted.